1. Art Field
The present invention relates to a composite dielectric material composition having a dielectric constant and low dielectric loss tangent suitable for use in high-frequency regions in particular, and a film, substrate, electronic part or molded or otherwise formed article using the same.
2. Background Art
To meet recent sharp increases in the quantity of information communications, there are growing demands for size and weight reductions, and fast operation of communications equipment and, hence, low-dielectric electrical insulating materials capable of meeting such demands are now in urgent need. In particular, the frequencies of radio waves used for hand-portable mobile communications such as earphones and digital portable phones, and satellite communications are in high-frequency bands covering from the MHz to GHz bands. Size reductions, and high-density packing of housings, substrates and elements are attempted on account of the rapid progress of communications equipment used as these communications means. For achieving size and weight reductions of communications equipment used in the high-frequency band region covering from the MHz to GHz bands, it is now required to develop an electrical insulating material with excellent high-frequency transmission characteristics combined with suitable low dielectric characteristics. In other words, a device circuit undergoes energy losses in the transmission process, which are called dielectric losses. The energy losses are not preferable because they are consumed as thermal energy in the device circuit, and discharged in the form of heat. In a low-frequency region the energy losses occur due to a dipole field change caused by dielectric polarization, and in a high-frequency region they occur due to ionic polarization and electronic polarization. The ratio between the energy consumed in a dielectric material and the energy built up in the dielectric material per cycle of an alternating field is referred to as a dielectric loss tangent, represented by tan xcex4. The dielectric loss is proportional to the product of a dielectric constant ∈ and the dielectric loss tangent of material. Consequently, tan xcex4 increases with increasing frequency in the high-frequency region. In addition, the quantity of heat generated per unit area increases due to the high-density packing of electronic elements. To reduce the dielectric loss of a dielectric material as much as possible, therefore, it is required to use a material having a small value for tan xcex4. By use of a low-dielectric polymeric material having a reduced dielectric loss, the dielectric loss and the generation of heat due to electrical resistance are reduced so that the risk of signal malfunctions can be reduced. Materials having reduced transmission losses (energy losses) are thus strongly desired in the field of high-frequency communications. For materials electrically characterized by electrical insulation and a low-dielectric constant, it has been proposed so far in the art to use a diversity of materials such as thermoplastic resins, e.g., polyolefin, vinyl chloride resin and fluorine base resin, and thermosetting resins, e.g., unsaturated polyester resin, polyimide resin, epoxy resin, bis-maleimidotriazine resin (BT resin), crosslinkable polyphenylene oxide, and curable polyphenylene ether.
When materials having a low dielectric constant are used as an electronic part (element) material, however, polyolefins such as polyethylene and polypropylene, like those set forth in JP-B 52-31272, have a grave disadvantage that their heat resistance is low although they have excellent insulation resistance as electrical properites. This is because they have a covalent bond such as a Cxe2x80x94C bond, and are free of a large polar group. For this reason, their electrical properties (dielectric loss, dielectric constant, etc.) become worse when they are used at high temperatures, Thus, such polyolefins are not preferable for use as an insulating film (layer) for capacitors, etc. The polyethylene and polypropylene, once they have been formed into film, are coated and bonded onto a conductive material using an adhesive agent. However, this method does not only involve a complicated process but also offers some problems in view of coating, for instance, because it is very difficult to make the thickness of the film thin.
The vinyl chloride resin has high insulation resistance and excellent chemical resistance and fire retardance, but it has the demerits of lacking-heat resistance as in the case of polyolefins, and having large dielectric losses as well.
Polymers containing a fluorine atom in their molecular chains, like vinylidene fluoride resin, trifluoroethylene resin, and perfluoroethylene resin, are excellent in terms of electrical properties (low dielectric constant, low-dielectric loss), heat resistance and chemical stability. However, one difficulty with such polymers is that, unlike thermoplastic resins, they cannot be heat-treated into formed articles or films due to their poor formability, and their poor ability to form coatings. Another disadvantage is that some added cost is needed for forming the polymers into devices. Yet another disadvantage is that the field to which the polymers are applicable is limited due to their low transparency. Such low-dielectric polymeric materials for general purpose use as mentioned above are all insufficient in terms of heat resistance because their allowable maximum temperature is below 130xc2x0 C. and, hence, they are classified as an insulating material for electrical equipment into heat resistance class B or lower according to JIS-C4003.
On the other hand, the thermosetting resins such as epoxy resin, polyphenylene ether (PPE), unsaturated polyester resin, and phenolic resin are mentioned for resins having relatively good heat resistance. As disclosed in JP-A 6-192392, the epoxy resin conforms to performance requirements regarding insulation resistance, dielectric breakdown strength, and heat-resistant temperature. However, no satisfactory properties are obtained because of a relatively high dielectric constant of 3 or greater. The epoxy resin has another demerit of being poor in the ability to form thin films. In addition, a curable modified PPO resin composition is known, which composition is obtained by blending polyphenylene oxide resin (PPO) with polyfunctional cyanic acid ester resins and other resins, and adding a radical polymerization initiator to the blend for preliminary reactions. However, this resin, too, fail to reduce the dielectric constant to satisfactory levels.
With a view to improving the epoxy resin having poor heat resistance, combinations of the epoxy resin with, for instance, phenol-novolak resin, and vinyltriazine resin have been under investigation. However, a grave problem with these combinations is some significant drop of the dynamic properties of the resulting films.
For the purposes of solving the above problems while the electrical properties are maintained, and specifically introducing improvements in the processability on heating, and close contact with or adhesion to copper or other metal conductors (layers), proposals have been put forward for copolymers of branched cyclo-ring amorphous fluoropolymer, and perfluoroethylene monomer with other monomers. However, although these copolymers may satisfy electrical properties such as dielectric constant, and dielectric loss tangent, yet their heat resistance remains worse under the influence of a methylene chain present in the high-molecular main chain. Never until now, thus, is there obtained any resin that can come in close contact with device substrates.
Among performance requirements for a low-dielectric-constant material excellent in dielectric properties and insulation resistance, there is heat resistance. That is, such a material can stand up well to a 120-second heating at a temperature of at least 260xc2x0 C. because a soldering step is always incorporated in a device fabrication process. Stated otherwise, the material should also be excellent in heat resistance, chemical stability such as alkali resistance, humidity resistance, and mechanical properties. Thus, the range of high-molecular materials capable of meeting such requirements is further limited. For instance, polyimide, polyether sulfone, polyphenylene sulfide, polysulfone, thermosetting polyphenylene ether (PPE), and polyethylene terephthalate are only known in the art. While these high-molecular materials are capable of forming thin films and coming in close contact with substrates, it is found that they are somewhat awkward.
With recent diverse progresses in electronic technologies, insulating materials used for electronic equipment, too, are being required to have diverse performances. Printed wiring boards in particular are used in a very wide range of applications and, hence, substrates thereof must now meet more and more requirements. Under such situations, there are also numerous requirements for dielectric properties.
For the purposes of fast transmission, high-characteristic impedance, thickness reductions of wiring boards, and crosstalk reductions in printed wiring boards, low-dielectric-constant wiring boards have been so far under development. For the purposes of forming delaying circuits on high-frequency circuit, microwave circuit or other wiring boards, achieving characteristic impedance matching in low-impedance circuit wiring boards, making wiring patterns fine, incorporating into hybrid circuits an element in which a substance itself has a capacitor effect, etc., on the other hand, high-dielectric-constant substrates are now required.
With recent progresses in information communication systems, the frequencies of radio waves used for hand-portable mobile communications such as earphones and digital portable phones, and satellite communications are in high-frequency bands covering from the MHz to GHz bands. Size reductions, and high-density packing of housings, substrates and elements are attempted on account of the rapid progress of communications equipment used as these communications means. Equivalent requirements are imposed on antennas used therewith. Thus, planar antennas used as high-frequency antennas are now fabricated by forming micro strip lines on dielectric substrates.
For the dielectric substrates for planar antennas, materials such as Teflon (∈r=2.2 to 2.7/1 GHz) or BT resin (∈r=3.3 to 3.5/1 GHz) having relatively low relative dielectric constants (∈r) have been used. With these materials, however, it is difficult to obtain high reliability because it is difficult to achieve size reductions and because the materials are susceptible to deformation due to heat and dielectric constant (∈r) changes due to temperature.
To reduce the size of planar antennas, therefore, the dielectric substrate used to this end must have such properties as high dielectric constant and low losses.
For this purpose, it has been proposed to use a substrate having a high dielectric constant, which is fabricated by adding ceramic powders having a high dielectric constant to resins for multilayered sheets or printed wiring boards, e.g., phenol resin or epoxy resin or low-dielectric-constant resins such as fluorine resin or polyphenylene ether resin to impregnate a glass cloth or glass unwoven cloth with the ceramic powders, drying the cloth together with the powders to form a prepreg, and laminating such prepregs together.
However, it is impossible to achieve dielectric loss tangent reductions only by adding the high-frequency ceramics having a high dielectric constant to general thermosetting resins such as conventional phenol or epoxy resin for multilayered sheets or printed wiring boards.
When a filler having a high dielectric constant is added to resins having a low dielectric constant, e.g., fluorine resin or polyphenylene ether resin, there is a dielectric loss tangent decrease. To make the dielectric constant high, however, it is required to increase the amount of the filler added, resulting in problems such as drops of the ability of the multilayered sheet to be drilled or cut, and large dimensional changes of the multilayered sheet upon drilling or cutting.
One object of the present invention is to provide a heat-resistance, low-dielectric-constant resin composition which possesses high heat resistance and a low coefficient of linear expansion, and is excellent in close contact with or adhesion to a metal conductor layer, capable of forming a thin film with a dielectric constant being selected from a relatively wide range, low in terms of dielectric loss, and excellent in insulating properties, and weather resistance and processability as well, and a film, substrate, electronic part or molded or otherwise formed article using the same.
Such objects are achieved by the inventions as defined below.
(1) A composite dielectric material composition comprising a heat-resistant, low-dielectric polymeric material (I) that is a resin composition comprising one or two or more resins having a weight-average absolute molecular weight of at least 1,000, wherein the sum of carbon atoms and hydrogen atoms in said composition is at least 99%, and some or all resin molecules have a chemical bond therebetween, and a filler (II).
(2) The composite dielectric material composition according to (1), wherein said chemical bond in said heat-resistant, low-dielectric polymeric material is at least one bond selected from crosslinking, block polymerization, and graft polymerization.
(3) The composite dielectric material composition according to (1), wherein said heat-resistant, low-dielectric polymeric material is a copolymer in which a non-polar xcex1-olefin base (co)polymer segment and/or a non-polar conjugated diene base (co)polymer segment are chemically combined with a vinyl aromatic (co)polymer segment, and is a thermoplastic resin which shows a multi-phase structure wherein a dispersion phase formed by one segment is finely dispersed in a continuous phase formed by another segment.
(4) The composite dielectric material composition according to (3), which is a copolymer with said non-polar xcex1-olefin base (co)polymer segment chemically combined with said vinyl aromatic (co)polymer segment.
(5) The composite dielectric material composition according to (3), wherein said vinyl aromatic (co)polymer segment is a vinyl aromatic copolymer segment containing a monomer of divinylbenzene.
(6) The composite dielectric material composition according to (4), wherein said copolymer in which sand non-polar xcex1-olefin base (co)polymer segment and/or said non-polar conjugated diene base (co)polymer segment are chemically combined with said vinyl aromatic (co)polymer segment is a copolymer chemically bonded by graft polymerization.
(7) The composite dielectric material composition according to (1), wherein said heat-resistant, low-dielectric polymeric material further comprises a non-polar xcex1-olefin base (co)polymer containing a monomer of 4-methylpentene-1.
(8) The composite dielectric material composition according to (1), which has a dielectric constant of at least 1.0 and a Q value of at least 100 in a high-frequency band of at least 1 MHz.
(9) The composite dielectric material composition according to (1), wherein said filler is in a fibrous state.
(10) The composite dielectric material composition according to (1), wherein said filler is a non-fibrous state.
(11) The composite dielectric material composition according to (1), wherein said filler is a high-frequency ceramic dielectric material.
(12) The composite dielectric material composition according to (11), wherein said high-frequency ceramic dielectric material is a titanium-barium-neodymium base material and/or a lead-calcium base material, and accounts for 50 to 95% by weight of said composite dielectric material composition.
(13) A film of at least 20 xcexcm in thickness, which is obtained using the composite dielectric material composition according to (1).
(14) A substrate obtained by lamination of films, each according to (13).
(15) A substrate obtained by coating a surface of a metal sheet with the composite dielectric material composition according to (1).
(16) The film according to (13), which is used in a high-frequency band of at least 1 MHz.
(17) The substrate according to (14), which is used in a high-frequency band of at least 1 MHz.
(18) An electronic part, which is obtained using the composite dielectric material composition according to (1) and used in a high-frequency band of at least 1 MHz.
(19) An article obtained by forming the composite dielectric material composition according to (1) into a given shape.